Modeling UX ursae majoris: An abundance of challenges

We present a system model for optical and far-UV spectra of the nova-like variable UX UMa involving a white dwarf, secondary star, gas stream, hot spot, and accretion disk using our code BINSYN and based on an initially adopted system distance. Calculated SED intensity data successfully fit successive tomographically extracted annuli longward of the Balmer limit but require a postulated "iron curtain" shortward of the Balmer limit that is applied to the annulus section closest to the secondary star, while postulated recombination emission fills in the model SED shortward of the Balmer limit and is applied to the annulus section more remote from the secondary star. The same model fits UBV 1954 light curves by Walker and Herbig. Fits to HST FOS spectra are approximate but require assumed time-variable changes in the SED. Comparable effects, possibly involving variable absorption, afflict FUSE spectra. Fits to IUE spectra by the model show time-dependent residuals that indicate changes in the accretion disk temperature profile, possibly indicative of a slightly variable Ṁ from the secondary star. Using model-based component light contributions and the improvement on the Bailey relation by Knigge we determine the system distance and mass transfer rate.